Method of making an insulated armature

ABSTRACT

An armature including a sleeve of insulating material bonded in place between the armature shaft and the armature laminations. The insulating sleeve may extend under the commutator if desired. A method of providing this armature is also described which comprises holding the laminations, the sleeve and the shaft in their relative positions and injecting a bonding material between the sleeve and the shaft and between the sleeve and the laminations.

6/1956 Hekelaar 336/233 X I Umted States Patent 1 1111 3,737,987Bednarski June 12, 1973 [5 METHOD OF MAKING AN INSULATED 2,541,047 21951 Frisbie et a1. 310 235 ARMATURE 3,477,125 11/1969 Schwartz 29/5962,818,517 12/1957 Loosjes 310/261 X [75] In nt r: Th d u Bednarski,Timonium, 3,447,011 5/1969 Amrein'et al 310 235 Md. FOREIGN PATENTS ORAPPLICATIONS [73] Ass1gnee. The Black and Decker 151,024 8/1955 SwedenhMdgnufacturmg Company Toll/5", 979,009 1/1965 Great Britain 310/43 [22]Filed: May 26, 1971 Primary Examiner-Charles W. Lanham AssistantExaminer-Carl E. Hall [21] Appl' 147l4l Attorney-Leonard Bloom, JosephR. Slotnik and Related US. Application Data Edward D. Murphy [62]Division of Ser. No. 878,825, Nov. 21, 1969, Pat. No. 7

3,639,789. 57 ABSTRACT 521 US. Cl. 29/596, 29/597, 29/598, An armatureincluding a sleeve of insulating material 310/43 3 10/261' bonded inplace between the armature shaft and the ar- 51 Int. Cl. H02k 15/00mature laminations- The insulating sleeve y extend [58] Field of Search29/598, 596; 310/42, under the commutator i desired. A method of provid-310/43, 235, 261, 217; 264/271, 272, 275 ing this armature is alsodescribed which comprises holding the laminations, the sleeve and theshaft in 5 Ref e i d their relative positions and injecting a bondingmaterial vUNITED STATES PATENTS between the sleeve and the shaft andbetween the 2 751 525 sleeve and the laminations.

2' Claims, 2 Drawing Figures PATENTEBJUN 1 2mm 3 737' 987 PRESSURIZEDADHESIVE INVENTOR THADDEUS E. BEDNARSKI ATTORNEY TO VACU U M SYSTEMMETHOD OF MAKING AN INSULATED ARMATURE This is a division of applicationSer. No. 878,825, filed Nov. 21, 1969, now US. Pat. No. 3,639,789.

This invention relates to double insulated armature shafts and isparticularly directed to a double insulated construction which is bothimproved and less expensive to manufacture.

. One present method of providing insulation between the shaft of anelectric motor and the stack of laminations in which the armaturewindings are placed is based on the injection and molding in place of amaterial which performs both the functions of bonding the laminations tothe shaft and of insulating the'laminations from the shaft. It isdifficult to obtain materials which adequately meet all of therequirements of this process without excessive cost. An even moresignificant expense of this process is the fact that the material mustbe molded in place within a highly complex press which holds the variouselements in the proper location and applies suitable heat and pressureso that an injected resin is molded in place. Suitable presses forperforming this operation are extremely expensive; in addition, only afew units can be processed at a time so that, for mass production, largenumbers of the presses are required with a consequent increase in thecapital investment required.

An alternative to this method is that of molding a sleeve around thearmature shaft, grinding it to an appropriate size and pressing it intothe center bore in the stack of laminations. While this processdecreases the expense of the press required for molding the sleeve, thetolerance requirements of the pressing operation are extremely high.These requirements apply to the size of the center bore, the size of themolded sleeve and the relative position of the sleeve and the stack asthe pressing is performed. Tolerance limitations on these steps areusually on the order of 0.001 inch or even less. Mass production toolingwhich can maintain these tolerances over extended periods of qualityproduction is extremely expensive. It is a primary purpose of thisinvention to provide a new armature construction which avoids thesedifficulties and the consequent expense while at the same time providingimproved results.

It is accordingly an object of this invention to provide a new andimproved insulated armature.

Another object of this invention is the provision of a new and improvedarmature which is less susceptible to breakdown of the insulationbetween the armature shaft and the laminations.

Another object of this invention is the provision of a new and improvedmethod of constructing armatures which is less complicated and lessexpensive than previous methods.

Further objects and advantages of this invention will become apparent asthe description and illustration thereof ensue.

Briefly, in accord with one embodiment of this invention, an armaturefor an electric motor is provided which includes a rotor having aplurality of windings and a central bore, a shaft located within thebore for providing a power output, an insulating sleeve disposed betweenthe rotor and the shaft and adhesive layers respectively affixing therotor to the sleeve and the sleeve to the shaft. In a particularembodiment, the sleeve comprises a glass cylinder and the adhesivelayers are of sufficient thickness to compensate for thermal andmechanical stresses between the rotor and the sleeve and between thesleeve and the shaft. In accord with another specific embodiment, thesleeve may comprise a paper cylinder.

This invention .will thus be understood from a consideration of thefollowing description and accompanying drawings in which:

FIG. 1 is a plan view, partially in cross-section, of an armatureconstructed in accord with the present invention; and

FIG. 2 is a cross sectional view of apparatus for performing the methodin accord with this invention.

In FIG. 1, an armature 10 is illustrated which comprises a stack oflaminations 11 having a plurality of slots 12 in which coils 13 ofinsulated wire are wound in accord with conventional practice. Each coilis attached to a conductive bar 14 of a commutator 15, the particulararmature illustrated being designed for use in a universal motor.

The laminations 11 are provided with a central bore 16 in which isdisposed a shaft 17. In use, an electromagnetic torque applied to thewindings causes the rotor to rotate and a power output is derived fromone end of the shaft 17 which is located within the bore 16.

In accord with the present invention, the shaft is insulated from therotor stack by means of a sleeve 18 of insulating material whichsurrounds the shaft and extends under the entire length of the stack.The sleeve is affixed to the shaft 17 and to the stack 11 by means ofadhesive layers 19 and 20. For example, in a preferred embodiment ofthis invention, the sleeve 18 comprises a glass cylinder while theadhesive layers comprise a room temperature vulcanizing silicon rubher.

A particularly significant advantage of this invention is derived fromthe method of assembly. Specifically, as 7 previously noted, othermethods require very complex and expensive equipment, either for holdingthe parts in place during molding or for meeting the tolerancerequirements of a pressing operation. The armature of the presentinvention can be constructed in simple, inexpensive apparatus which canreadily be adapted to the manufacture of large quantities. For example,FIG. 2 illustrates schematically a suitable fixture for the performanceof the method of this invention. The supporting structure 21 includesrespective openings 22, 23 and 24 for receiving the 'shaft, sleeve andlaminations. A cover member 25 is clamped in place to secure thelaminations and to hold the shaft and sleeve in alignment. Vacuum lines26 are preferably used to prevent the entrapping of air at the base ofthe unit; appropriate means may of course be provided to seal off theseopenings when the adhesive is introduced.

The adhesive is supplied from a reservoir of liquid adhesive. A valve 27supplies the adhesive to nozzles 28 and 29 which respectively inject theliquid adhesive into the spaces between the laminations and the sleeveand between the sleeve and the shaft. After the adhesive is introduced,curing may be performed either by time alone or by the application ofheat to increase the speed of curing.

Even if a source of heat is provided to assist in curing the adhesive,the fixture and tooling for performing this method are much simplierthan that required by previous methods. For example, the tolerancerequirements for the relative size and position of the three elementsneed only be maintained within several thousandths of an inch. Althoughthis is still a relatively small space, the difference in the toolingrequired to maintain this tolerance as compared to that of less than0.001 inch may reduce the cost by a factor of one-third to onefifth. Asimilar comparison also applies when considering this equipment ascompared to, that required for performing molding of a material whichmust function both as an adhesive and as an insulator.

As previously noted, the subject invention not only enables the cost ofmanufacture to be substantially reduced, but it also provides a moreeffective insulative barrier than previous methods. Specifically, if thesingle layer of previous constructions is provided, a breakdown in thatmaterial which occurs due to a particular cause is frequently of a typewhich can readily propogate across the width of the material. This isdue to the fact that the cause of the initial breakdown may continue toaffect the same material in the same way. In a construction according tothe present invention, however, this possibility is avoided becausethere are two different materials arranged in three layers between theshaft and the stack. Thus, a cause of failure in one of the layers isunlikely to have any effect at all on the adjacent layer of the othermaterial. For example, if breakdown of the polymeric adhesive materialoccurs due to age in either of the adhesive layers, it may propogaterapidly across the width of that layer but it will not propogate throughthe sleeve since the sleeve is chemically different and is not affectedby the same conditions. On the other hand, if a rupture occurs in thesleeve, it will not affect the adhesive layers on either side since theadhesive is a relatively resilient material and will withstand therupturing stress. Thus, the insulation provided by the illustratedconstruction is substantially more effective than that provided byprevious constructions.

In the preferred embodiment, the insulating sleeve is glass and theadhesive material is a room temperature vulcanizing rubber. Thisparticular embodiment is of interest due to the fact that the dielectricstrength of glass is so high that the insulation requirements such as,for example, those of Underwriters Laboratories, Inc., are more thanfulfilled by the glass cylinder itself and any insulating effectprovided by the rubber is, in effect, a bonus. A potential difficultywith this embodiment is the possibility that the glass may break. Inaccord with this invention, this is overcome by providing a sufficientlythick and sufficiently resilient layer of adhesive on each side of thesleeve so that any stresses introduced between the shaft and the stackwhich might tend to fracture the glass are taken up by the adhesive. Forexample, these stresses may be either thermal, due to a difference inthe amount of expansion under heat of the glass cylinder as compared tothe metal stack and shaft, or mechanical, due to the twisting momentbetween the rotor stack and the shaft.

Another embodiment of this invention which also enjoys the advantageslisted above is that in which the sleeve is made of paper of asufficient thickness and dielectric strength so thatthe electricalinsulative requirements are met. In this embodiment, since the sleeve isnot susceptible to breaking, even wider tolerance in manufacture can bepermitted since the adhesive need only be sufficient to bond theelements together. Thus, the sleeve can be positioned rather looselyaround the shaft and the adhesive can be injected under sufficientpressure to insure that all of the spaces in both annular openings arefilled. Of course, other insulative materials may be selected ifdesired. It is also noted that, to meet specific requirements, variousmodifications in the properties of these materials may be desired. Forexample, by providing a certain amount of resilience in the adhesivematerial, a certain amount of relative rotation may be permitted betweenthe stack and the shaft under locked-rotor condition. This may be usedto relieve strain which would otherwise break the gears in the output ofthe tool or other device in which the motor is used.

In another embodiment, the sleeve may be paper or cardboard ofsufficient thickness to provide the required dielectric strength. Inthis case, the adhesive layers need only be sufficient to insure bondingof the three elements of the structure together.

Regardless of the material selected, it is preferred that the sleeve inthe construction of this invention be a continuous cylindrical body.While it is possible to provide multiple elements which, when placedtogether approximate a cylinder, this introduces difficulty in aligningthe pieces and therefore increases the cost and complexity ofmanufacture. In addition, the adhesive may not adequately fill theinterface between the pieces and, even if it does, it permits thepossibility of propogation of a fault through one material, thusdefeating a particularly desirable feature of this invention.

While several embodiments of this invention have been shown anddescribed, it will be apparent to those skilled in the art that manychanges and modifications may be made from the specific illustrationswithout departing from the spirit of this invention in its broaderaspects as defined by the appended claims.

I claim:

1. The method of producing a double-insulated armature for. an electricmotor, comprising the steps of:

providing an armature shaft, and providing a stack of armaturelaminations having a bore and further having a plurality of axiallyextending circumferentially spaced winding slots,

further providing a hollow cylindrical insulating sleeve, the sleevehaving an axial length which is greater than the length of the stack oflaminations, and further having a radial wall thickness which issubstantially less than the diameter of the armature shaft; I holdingthe shaft, sleeve, and stack in concentric relationship with respect toeach other, whereby the sleeve is disposed radially between the shaftand the bore in the stack with respective radial clearancestherebetween, and whereby the sleeve extends axially beyond the ends ofthe stack; introducing a first curable adhesive between the shaft andsleeve while the shaft and sleeve are in said concentric relationshipand spreading the adhesive substantially along the entire axial lengthof the interior of the sleeve and beyond the ends of the stack to createa thin annular layer of adhesive between the shaft and sleeve, andcuring the adhesive whereby the adhesive bonds the sleeve to the shaft,introducing a second curable adhesive between the sleeveand the bore inthe stack while the sleeve and the stack are in concentric relationshipand spreading the adhesive substantially along that portion of the axiallength of the exterior of the sleeve, as defined by the length of thestack, to create a thin annular layer of adhesive between the stackcommutator. and the sleeve, and curing the adhesive whereby 2. Themethod claimed in claim 1 wherein said step the adhesive bonds the stackto the sleeve, of introducing the second curable adhesive betweensecuring a commutator on the shaft, the sleeve and the bore in the stackis performed simulwinding the armature by providing coils in the re- 5taneously with the step of introducing the first curable spectivewinding slots of the stack, and adhesive between the shaft and thesleeve. connecting the coils to respective portions of the

1. The method of producing a double-insulated armature for an electricmotor, comprising the steps of: providing an armature shaft, andproviding a stack of armature laminations having a bore and furtherhaving a plurality of axially extending circumferentially spaced windingslots, further providing a hollow cylindrical insulating sleeve, thesleeve having an axial length which is greater than the length of thestack of laminations, and further having a radial wall thickness whichis substantially less than the diameter of the armature shaft; holdingthe shaft, sleeve, and stack in concentric relationship with respect toeach other, whereby the sleeve is disposed radially between the shaftand the bore in the stack with respective radial clearancestherebetween, and whereby the sleeve extends axially beyond the ends ofthe stack; introducing a first curable adhesive between the shaft andsleeve while the shaft and sleeve are in said concentric relationshipand spreading the adhesive substantially along the entire axial lengthof the interior of the sleeve and beyond the ends of the stack to createa thin annular layer of adhesive between the shaft and sleeve, andcuring the adhesive whereby the adhesive bonds the sleeve to the shaft,introducing a second curable adhesive between the sleeve and the bore inthe stack while the sleeve and the stack are in concentric relationshipand spreading the adhesive substantially along that portion of the axiallength of the exterior of the sleeve, as defined by the length of thestack, to create a thin annular layer of adhesive between the stack andthe sleeve, and curing the adhesive whereby the adhesive bonds the stackto the sleeve, securing a commutator on the shaft, winding the armatureby providing coils in the respective winding slots of the stack, andconnecting the coils to respective portions of the commutator.
 2. Themethod claimed in claim 1 wherein said step of introducing the secondcurable adhesive between the sleeve and the bore in the stack isperformed simultaneously with the step of introducing the first curableadhesive between the shaft and the sleeve.